Fault-locator for electric cables.



H. M. STOLLER.

FAULT LOCATOR FOR ELECTRIC CABLES.

APPLICATION FILED DEC. 24, 1913.

1,170,017. Patented F0111, 1916.

2 SHEETS-SHEET I.

W/fnesses: /m/e/72o/1' M Hugh M 570//er,'

Ar/y

H. M. STOLLER.

FAULT LOCATOR FOR ELECTRIC CABLES.

APPLICATION FILED 0512.24, 1913.

1,170,017. Patented Feb.1, 1916.

2 SHEETSSHEET 2.

l/V/fnesses: /nve/7f0r.'

Hug/2 M Sid/er HUG-H MONTGOMERY STOLLER, OF NEE/V YORK, N. Y.,ASSIGNOJRJ, BY MESNE assrerr- MENTS, TO WESTERN ELECTRIC COMPANY,INCQBPORATED, A CORPQPLATTQN 0F FAULT-LOCATOB FOR ELECTRIC CABLES.

LFNMMUZ'.

, [application filed December 24, 1913.

To all wiwm it may concern:

Be it known that T, HUGH MONTGOMERY S'roLLnn, a citizen of the UnitedStates, residing at New York, in the county of New York and State of NewYork, have invented a certain new and useful improvement inFault-Locators for Electric Cables, of which the following is a full,clear, concise, and exact description.

This invention. relates to the location of faults in electric cables.Tts objects in general are the attainment of high efficiency in testingthe field of the cable conductors, and the production of an exploringcoil capable of ready adaptability and easy manipulation in a variety ofways, accorchng to the nature and location of the fault and the positionof the cable.

The invention has especial application to the location of faults intelephone cables, that is to say, to cables comprising twisted pairs ofconductors, a special object being toprovide an exploring coil sensitiveto currents flowing in metallic circuits through the twisted pairs,whereby short-circuits in the pairs may be accurately located.

Cables may be classified generally according to their location orposition as aerial and underground, and they are usually provided with aprotecting lead sheath. Telephone cables are ordinarily made up oftwisted pairs of conductors individually wrapped loosely with paper sothat a substantial air space as well as the paper separates andinsulates them from each other and the sheath. Trouble which occurs attimes in such cables is due to various causes and is usually manifest bya breaking down or lowering of the insulation resistance of one or moreof the conductors. At such times it is important that the fault beaccurately located and corrected quickly, without unnecessary damage tothe cable or its sheath and with the least possible interruption toservice of the cable conductors which are not in trouble. The mostfrequent faults in cables, to the location of which this invention isapplicable, may be classified as (1) grounds to conductors, 2'. 6., toconductors of which the insulation to the sheath is low or "has brokendown, (2) crosses between conductors not of the same pair, and (3) shortPatented Fe "2. i, 19b8,

Serial Il'o. 803,561.

circuits between conductors of the same pair. These faults may be incombination and caused by moisture entering the cable, and they are insuch cases usually ter 7 wet spots. In order to prepare the faultyconductor or conductors for the location of the fault, a source ofintermittent current which may be d tected audibly by a telephone receiver, is connected thereto and an exploring coil in circuit with thecurrent 1g instrument is carried along the cable from point to pointuntil the fault is located. Then the sheath is opened at that point, thetrouble cleared, and the sheath repaired.

A high degree of eiiiciency is attained in accordance with thisinvention by the use of an exploring coil which is provided with adepression in its pole piece transverse to the axis of the magnet coil,"5. 6., to the central line of the core about which the convolutionswill fit the surface of the cable with the said axis transverse to thecenter line or axis of the cable. This form of coil is useful whentesting for crosses or grounded conductors. The core is preferablylaminated in planes parallel to the axis of the coil and also to theaxis of the cable. This core may be either substantially rectangular or"cl-shaped. The latter is preferred because the U-shape renders itadaptable for uses such as the location of faults in short-circuitedpairs, as well as the location of ordinary crosses and grounds. TheU-shaped core may be provided with two coils, one on each leg thereof,and when its two coils are properly connected together and in circuitwith the current detecting instrument, the device operates in the samemanner as a single simple rectangular core with a single coil forlocating crosses and grounded conductors. Both of the free pole facesare provided with transverse grooves parallel to the yoke, or areotherwise so shaped or fitted that when the device is applied to thecable it will fit snugly to the surface with the two free pole piecespresented to, that is to say pointing toward, the axis of the cable atdifferent positions longitudinally thereof. There is provided for thisU-shaped exploring magnet and its two coils, a casing and two sets ofterminal switch members, each set having one member for each end of eachcoil. The current detecting instrument is preferably connected byaflexible cord with a third set of terminal switch members. The lattermay be in the form of twin plugs and the former in the form of socketsor jacks. The connections of the coils to the two sets of switch membersare such that when the plug is inserted in the sockets of one set, thetwo coils are connected together in circuit with the detectinginstrument, and when inserted in the sockets of the other set aresimilarly connected with that instrument, but with one of the coils inreverse position in the circuit. Preferably the two coils are in eachcase connected in parallel with each other in the circuit of theinstrument. The parallel arrangement simplifies the switch structure.

When using the exploring magnet to locate crosses or grounds, the twocoils are connected together in such a way that a like magnetic effecton the two free pole pieces will produce a cumulative effect in thecurrent detecting instrument, but when using it for locatingshort-circuits the coils are oppositely connected, and unlike magneticeffects on the two poles in this case, will produce a cumulative effectin the detecting instrument.

To adapt the exploring magnet for 10- cating short-circuits it isconstructed so that the distance between the centers of the two polepieces is approximately equal to the distance between the centers ofadjacent half twists in the cable conductors. Preferably also the widthof each pole face is approximately one-half the length of the halftwists.

In testing for a fault in an aerial cable which is incased in a metallicsheath, it is necessary to distinguish between the intermittent currentapplied to the faulty conductor and stray currents which may be flowingin the sheath of the cable. For that reason the exploring magnet isapplied to the cable symmetrically, that is to say, with its yokeparallel to the axis or center line of the cable, and with the free endsof its poles pointing transversely thereto. In this position theinstrument will not respond to sheath currents with either manner ofconnection of the two coils in the circuit of the detecting instrument.Therefore the detecting instrument will respond to the intermittentcurrent in the faulty conductor when the exploring magnet is applied tothe cable at any point between the point of application of the currentand the point where the trouble has occurred, and its non-response inpassing the point of trouble enables the tester to locate the faultaccurately.

In testing for grounds or crosses in underground cables and in othercables where sheath currents are not troublesome, it may be desirable toapply the exploring magnet with its yoke crosswise to the direction ofthe cable and with the pole pieces partly straddling it, that is to say,pointing toward either side of it. Accordingly, the inner corners of thepole pieces of the device are flattened so that the device will fit thecable in this position also. When used in this way, the two coils are soconnected that opposite magnetic effects on the two pole pieces willproduce a cumulative current effect in the detecting instrument.

For a more complete understanding of this invention, reference may behad to the accompanying drawings wherein- Figure 1 is a view inperspective of the exploring coil and associated set of terminal switchmembers; Fig. 2 is a view partly in section on line 22 of Fig. 3; Fig. 3is a view on line 38 of Fig. 2; Fig. 4 is a View partly in section ofthe associated set of switch terminal members; Fig. 5 is a diagram ofconnections between windings of the exploring coil and two sets ofterminal switch members; Fig. 6 is a view of the exploring coil, thedetecting instrument, the source of testing current, the circuitconnections and the position of the exploring coil with respect to anaerial cable when testing for a short-circuit therein. Fig. 7 is a viewof the exploring coil, the detecting instrument, the source of testingcurrent, the circuit connections and the position of the exploring coilwith respect to an aerial cable when testing for a grounded conductortherein, and Fig. 8 is a view of the exploring coil, the detectinginstrument, the source of testing current, the circuit connections andthe position of the exploring coil with respect to an underground cablewhen testing for a grounded conductor therein.

As shown in the drawings, the exploring coil may comprise a U-shapedmagnet core having a yoke 10 and pole pieces 11 and 12 with anenergizing coil 13 mounted on pole piece 11, and an energizing coil 14Lmounted on pole piece 12. In order to reduce core losses, the magnet ispreferably built up of laminations 15 held between plates 16 and 17, thelaminations and the plates being secured together by means of rods 18.To permit free passage of the flux through the magnet in a directionparallel to the yoke 10, the magnet is built up with the laminations 15parallel to said yoke. In orderthat the magnet core may fit the cablewhen presented thereto with the yoke 10 of the magnet parallel with theaxis of the cable, the free ends of the pole pieces 11 and 12 areprovided with depressions 19 and 20, respectively, said depressionsbeing parallel to the yoke 10 and the laminations 15 and transverse tothe axes of the coils 13 and 14.

In order that the magnet core may fit the inner corners of the polepieces 11 and 12 are flattened, as at 25. In order that the coils 13 and14 may be protected, the magnet core may be provided with a casing 26 ofinsulating material. It is at times desirable to mold this casing ontothe magnet core, and in order that said core may be held in a casing soformed, the core upon each side thereof and near the lower side of theyoke 10, is provided with a bar 27, said bars being secured to the coreby means of the rods 18. The top of the casing may be covered with aplate 23 of non-magnetic material, which is secured to said casing bymeans of screws 29, 29. To prevent a closed secondary circuit beingformed in this plate 28, said plate is slotted, as at 30 and 31.

In each end of the casing 26 there is provided a set of terminal switchmembers 35, each set being composed of individual members 36, 37, 38 and39. To these individual members are attached the leads from the twocoils 13 and 14. As shown in Fig. 5, the leads from the coils 13 and 14terminate in one position in the individual members of the set at oneend of said casing, while at the other end thereof the position of theleads from coil 13 is reversed. As shown in Fig. 1, each two of theindividual members may conveniently form a jack adapted for thereception of another set of terminal switch members 45, which mayconveniently be in the form of twin plugs associated with a. currentdetecting instrument 52 (Figs. 6, 7 or 8) by means of a cord 53. Thisset of terminals 45 is composed of two members 46 and 47, which aremounted in a block 48 of insulating material. This block may be providedwith openings 49, 49 for the admission of cord conductors 54 and 55 tobe connected to the individual members 46 and 47, respectively. Theremay also be provided in the block 48, a ring 50 to which may be attacheda stay-cord 56 for relieving the conductors 54 and 55 from undue strain.The casing 26 which incloses the magnet core and coils of the exploringcoil, may also be provided with a ring 51 to which may be attached thestay-cord 56 so that the exploring coil and the associated set ofterminal switch members may be secured one to the other. Current may besupplied to the faulty conductor from any suitable apparatus, such, forexample, as that shoWn in Figs. 6, 7 or 8. The apparatus there shownconsists of a transformer 61, to the secondary 62 of which may beconnected the faulty conductor or conductors. One terminal of a battery63 is connected to the primary 64 of the transformer 61. The other sideof the battery is connected to a switch arm 65, which is adapted to makecontact with either terminal 66 or 67. The terminal 66- is connected tothe normally closed back contact 68 of the transformer 61. The armature69, controlled by the energization of the primary winding 64 of thetransformer,.is connected to said primary winding. One side of thebattery 63 is connected to the winding of an electromagnet 70. The otherend of the winding of the electromagnet 70 is connected to back contact71 of the electromagnet 70. A contact arm 72 of said electromagnet ispermanently connected to the terminal 67 and normally rests against backcontact 71. The electromagnet 70 is also provided with a front contact 73, which is permanently connected to the back contact 68 of thetransformer 61. Attraction of armature 74 opens contact 71, 72 and makescontact 72, 73. If an alternating current is desired on the conductorsin which there is a fault, the switch arm is moved to make contact withterminal 66 in which case a circuit is closed which may be traced as follows: from one terminal of battery 63, through switch arm 65, terminal66, back contact 68,armature 69, transformer primary 64, back to theother side of battery 63. Current flowing in this circuit energizesprimary winding 64 which thereupon causes the attraction of armature 69,opening contact 68. v Vinding 64 is thereupon deenergized, causing thearmature 69 to be retracted and again closing the circuit. Theconsequent energizing and deenergizing of the primary 64 of thetransformer 61, causes an alternating current to be sent out from thesecondary 62 of the transformer 61. Should an intermittent alternatingcurrent be desired on the conductor which is being tested, the switcharm 65 is then moved to make contact with terminal 67. Under suchconditions a circuit is established which may be traced as follows: fromone side of battery 63, through switch arm 65, terminal 67, contact arm72, back contact 71, winding of the electromagnet 70, back to the otherside of battery 63. Current flowing in-this circuit causes theenergization of electromagnet 70, which causes the attraction of itsarmature 74, whereupon contact 71, 72 is broken and contact 72, 73 made,establishing 1 plained. When back contact 71 was broken, due to theattraction of armature 74, the circuit through electromagnet 70 wasbroken, and the armature 74 was retracted. The attractlon and retractionof the armature 74 causes an intermittent alternating current to be setup in the secondary of the transformer.

In Fig. 6 there is represented a cable having a lead sheath 60 in whichis incased a number of pairs of conductors, one pair of which is made upof conductors 80 and 81, which are short-circuited at the point 82. Themanner of connecting the current supplying apparatus to this cable, andthe manner in which the magnet coils of the exploring coils areconnected in circuit with the current detecting instrument, as well asthe position in which said exploring coil is held with respect to thecable, will now be described.

The terminals of the secondary 62 of the transformer 61 are connected tothe two conductors 80 and 81. With these conductors connected to thesecondary of the transformer and the switch arm 65, closed at eitherterminal 66 or terminal 67, the direction of flow of current at someinstant from the transformer secondary along the conductors 80 and 81may be as indicated by the arrows. Considering this direction of flow ofcurrent, it will be seen that, in each half convolution o the twoconductors of the pair, the current is flowing in one direction in onconductor, and in the opposite direction in the other conductor. It willbe seen that, in effect, each half convolution of the two conductorsforms a closed loop in which there is a flow of current. Furthermore itwill be seen that in two adjacent loops, the direction of the flow ofcurrent around the loop is opposite. The direction of the lines of forceset up by the flow of current in two adjacent loops will, therefore, beopposite, and

, in the case supposed will be as indi- .c'ated by the letters N and S.It will now be supposed that the exploring coil is presented to thecable with its magnet yoke 10 parallel to the axis of the cable so thatthe depressions in its pole pieces 11 and 12 will fit the surface of thecable. Furthermore it will be supposed that the pole piece 11 isimmediately oppositethe loop whose magnetic field is designated S, andthe pole piece 12 is immediately opposite the loop whose magnetic fieldis designated N. The lines of force set up by current in the loop Swill, upon cutting the turns of the coil 13, which is carried by thepole piece 11, set up a flow of current in said coil in the directionindicated by the arrows. The lines of force set up by current flowing inthe loop N will, upon cutting the turns of the coil 14:, which iscarried by the pole piece 12, set up a flow of current in said coil inthe direction indicated by the arrows. In order, therefore, that thecurrents in the two coils 13 and 14; may cooperate to produce an effectin the current detecting instrument 52,

the said coils will have to be connected in circuit with said detectinginstrument in the manner indicated in Fig. 6. Referring to Fig. 5 inconnection with the manner in which the coils should be connected incircuit with the current detecting instrument in order to locate ashort-circuit, as illustrated in Fig. 6, the twin plugs 45 should beinserted in the jacks of end B of the exploring coil. It will beobserved that the direction of the fluxes and of the flow of currentabove referred to are instantaneous directions and these are continuallychang ing. As the exploring coil is moved along the cable the directionof flow of current in the coils 13 and 1+1 and in the current detectinginstrument in circuit therewith, will change relative to theinstantaneous direction of flow of current in the conductors and 81.Current will be detected by the current detecting instrument when theexploring coil is presented to the cable at points between the point ofapplication of the current and the point at which the conductors areshort-circuited. Since there is no current flowing in the conductorsbeyond the point of short circuit, in moving the exploring coil beyondsaid point, no current will be detected by the current detectinginstrument.

In Fig. 7, there is represented an aerial cable. the conductor of whichis grounded to the sheath ()0 at a point 86. One lead of the transformersecondary 62 is connected to the conductor 85. and the other leadtherefrom is connected to the sheath ($0. The exploring coil ispresented to the cable in the same manner as above described inconnection with the locating of a short-circuit. Closure of the circuitthrough battery ()3 and transformer primary G1 at either terminal 66 orterminal 67 will cause a How of alternating current from the transformersecondary 62, through the conductor 85.

grounded connection 86 and the cable sheath 87 back to the transformersecondary (32. The direction of flow of current at some instant throughthe transformer secondary (32. the faulty conductor 85 and the sheath60, is as indicated by the arrows adjacent thereto. In this case a fluxis set up due to the flow of current in the cable sheath 60, and anotherdue to the flow of current in the faulty conductor 85. The direction ofthe flux due to current in the cable sheath 60, is concentric with thesheath, and when the magnet core of the exploring coil is presented tothe cable in the manner above explained, the axes of the coils 13 and 11will pass through the center of the cable. Each turn of wire in eachcoil will lie in a plane perpendicular to the axis of the coil. Considerany line of flux concentric with the sheath which intersects this plane.This line of flux will lie in a plane perpendicular to the plane of theturn of wire and the planes will intersect in a straight line. Thisstraight line will pass through the circumferences formed by the turn ofwire and the line of flux. The two points formed by the intersection ofthe line with the circum ference described. by the line of flux will bewholly within or wholly without the points formed by the intersection ofthe line with the circumference of the turn of wire. Therefore, therewill be no interlinkage between any concentric line of flux and any turnof wire. Hence it follows that the lines of flux, due to current in thecable sheath, will have no effect whatever on said coils. The flux setup by current in the faulty conductor 85 is not concentric with thecable sheath and a portion thereof will, therefore, interlink with theturns of the coils 13 and 1d and produce a flow of current therein.Assume that the current in the faulty conductor 85 is flowing in thedirection indicated by the arrows. When the magnet core of the exploringcoil is presented to the cable at points between the point ofapplication of the current and the point 86, the flux acting upon thecoils 13 and 14, due to the current in the faulty conductor 85, will bein the same direction, indicated by the letters S, S. The cutting of theturns of the coils 13 and 1% by this flux will set up a flow of currentin each coil in the directions indicated by the arrows. In order,therefore, that the currents flowing in the coils 13 and 14 maycooperate to produce an effect in the current detecting instrument 52,the leads from said coils must be connected in circuit with said currentdetecting instrument 52 in the manner indicated in Fig. 7. Referring toFig. 5 in connection with the manner in which the coils should beconnected in circuit with the current detecting instrument 52 in orderto locate a grounded conductor in an aerial cable, as illustrated inFig. 7, the twin plugs 45 should be inserted in the jacks of end A ofthe exploring coil. lvith a reversal of the direction of flow of currentthrough the faulty conductors, the direction of the flux set up therebyand the resulting flow of current in each of the coils 1-3 and 14 willbe reversed. It is obvious that after passing the point 86 at which theconductor 85 is grounded to the sheath, there will be no flow of currentin said conductor. Since the detecting circuit as previously explainedis affected by conductor current only, there will be no effect producedwhen the exploring coil is presented to the cable beyond the point 86.

In Fi 8 there is represented an underground cable in which there is aconductor 87 grounded to the sheath at a point 88. It may be stated thatthere is a continuous ground on the cable sheath of an underground cablethroughout its entire length for the ducts through which said cable runsform a path to ground. Therefore, when one lead from the transformersecondary 62 is connected to the cable sheath 60 and the other to thefaulty conductor 87, the current on entering the cable sheath 60 atpoint 88 will find a parallel path to ground and, in fact, will find aninfinite number of parallel paths to ground from the cable sheath. Infact, the number of these paths will be so great that upon reaching apoint removed by only a very short distance from the point at which thecurrent enters the cable sheath, there will be an inappreciable flow ofcurrent in the cable sheath, the bulk of the current having found itsway through the aforesaid parallel paths to ground. The said currentwill traverse the path through ground to a point close to the point atwhich the lead from the transformer secondary 62 is connected to thesheath 60. The current will then begin to find its way back to the cablesheath, through an infinite number of similar parallel paths and thenback to the transformer secondary 62. It has been found, therefore, thatthroughout the major length of the underground cable having a faultyconductor therein, the inappreciable flow of current in the sheath maybe neglected, and the exploring coil presented to the cable in themanner indicated in Fig. 8 so as to obtain the greatest efficiency. Theonly current which need be considered is that flowing in the conductor87. When the direction of flow of current in the conductor 87 is asindicated by the arrow, the flux produced thereby at any one instantwill, upon opposite sides of the conductor 87, be opposite as indicatedby the letters N and S. To obtain the maximum efiiciency, the magnetcore of the exploring coil should be presented to the cable with theyoke of said core transverse to the axis of the cable and with theflattened inner corners of pole pieces 11 and 12 fitting the cablesheath as shown in Fig. 8. With the magnet core presented to the cablein this position and with the instantaneous directions of the fluxproduced by current in the conductor 87 as indicated by the letters Nand S, the current set up in the coils 13 and 1%, due to the cutting ofthe turns of said coil by said flux, will have a direction of flow asindicated by the arrows. in order that the currents flowing in the coils13 and 1d may cooperate to produce an effect in the current detectinginstrument 52, the coils should be connected in circuit with saidcurrent detecting instrument in the manner indicated in Fig. 8.Referring to Fig. 5 in connection with the manner in which the coilsshould be connected in circuit with the current detecting instrument 52in order to locate a grounded conductor in an underground cable, asillustrated in Fig. 8, the twin plugs axis of the coil and adapted tofit the surface of the cable.

2. A device for exploring the field of cable conductors, comprising acoil with a laminated magnet core having in its pole face a depressiontransverse to and intersecting the axis of the coil and adapted to fitthe surface of the cable, the laminations of said magnet being in planesparallel to said axis and also to said depression.

3. In a fault locator for electric cables, the combination with acurrent detecting instrument and a coil in circuit therewith, of amagnet core for said coil having in its pole face a depressiontransverse to and intersecting the axis of the coil and adapted to fitthe surface of the cable.

4. In a fault locator for electric cables,

' the combination with a current detecting instrument and a coil incircuit therewith, of a laminated magnet core for said coil having inits pole face a depression transverse to and intersecting the axis ofthe coil and adapted to fit the surface of the cable, the laminations ofsaid magnet being in planes parallel to said axis and also to saiddepression.

5. A device for exploring the field of cable conductors comprising aU-shaped magnet core and a winding on each leg thereof, said core havingin its pole faces depressions parallel to the yoke thereof and adaptedto fit the surface of the cable.

6. A device for exploring the field of cable conductors comprising aU-shaped laminated magnet core and a winding on each leg thereof, saidcore having in its pole faces depressions parallel to the yoke thereof,adapted to fit the surface of the cable, and the laminations of saidcore being in a direction parallel to the plane of said U-shaped core.

7. A fault locator for electric cables comwindings in parallel and insaid circuit with said device and for reversing at will the connectionsof one of said windings with respect to the other.

9. A device for exploring the field of cable conductors, comprising aU-shaped magnet core, adapted to fit the surface of the cable with itsfree poles presented to the axis of the cable at different pointslongitudinally thereof, two coils, one on each leg of said core, acasing for said coils and core, and two like sets of switch terminalscarried by said casing, each set comprising terminals for said coils andthe terminals for one of said coils being reversely positioned in thetwo sets.

10. A device for exploring the field of cable conductors, comprising aU-shaped electromagnet having the free pole pieces shaped so as to fitthe surface of the cable when presented thereto, with the yoke of saidmagnet either parallel with, or transverse to, the axis of the cable.

11. A device for exploring the field of cable conductors, comprising aUshaped electromagnet having in the surface of its pole piecesdepressions parallel with its yoke and the inner corners of said polepieces being flattened, whereby the electromagnet will fit the surfaceof the cable when said pole pieces are presented thereto with the yokeof said magnet either parallel with or transverse to the axis of thecable.

In witness whereof, I hereunto subscribe my name this 22d day ofDecember, A. D. 1913. i

HUGH MONTGOMERY ST'OIJLER.

Witnesses NANON E. TUTHILL, ALIcE HAZLEY.

